[0001] This invention relates to the substantial removal of volatile substances from polyphenylene
ether or polyphenylene ether/polystyrene compositions and, more particularly, to the
reduction of volatile substances in an extruder comprising multiple stages of water
injection followed by vacuum venting.
BACKGROUND OF THE INVENTION
[0002] Polyphenylene ethers are a class of polymers which are widely used in industry, especially
as engineering plastics in applications which require such properties as toughness
and heat resistance. For many such applications polyphenylene ether resins are blended
with various types of polystyrene resins to improve their processability. Recently
it has become necessary to produce such compositions which are both substantially
odorless and tasteless for food contact applications. It is therefore necessary that
the polyphenylene ether or polyphenylene ether/polystyrene composition be substantially
free from any volatile materials which have undesirable odors or would otherwise harm
the food. Materials of this kind which are known to be present in polyphenylene ether
or polyphenylene ether/polystyrene resins include toluene, dialkylamines such as di-n-butylamine,
which are components of the catalyst used in preparing polyphenylene ether resins;
styrene monomers, from degradation of any styrene resin and other by-products resulting
from polyphenylene ether resin synthesis. In the case of poly(2,6-dimethyl-1,4-phenylene
ether); 2,4, 6-trimethylanisole, 7-methyldihydrobenzofuran, 2,3-dihydrobenzofuran,
2,6-dimethylcyclohexanone and 2-ethylhex-2-enal are commonly present. Removal of
sources of volatile odoriferous amines and oxygenated species is especially important
because they are detectable in human organoleptic tests even in very low quantities.
[0003] Methods are known, to those skilled in the art, for removing volatile substances
from polyphenylene ether or polyphenylene ether/polystyrene resins during vented extrusion,
with or without the injection of water into the melt. For example, Kasahara et al.,
U.S. 4,369,278 extrudes polyphenylene ether and rubber reinforced polystyrene in a
single pass, single stage vacuum vented extruder with optional water injection; Newmark,
U.S. 3,633,880, extrudes plastic materials, which could include polyphenylene ether,
in a single pass through an extruder with multiple vents and employs a specially designed
screw to compress and decompress the melt aiding devolatilization without employing
water. Commonly assigned pending U.S. Patent Application, Serial No. 156,046 filed
February 16, 1988 (Attorney's Docket RD-18,017), extrudes polyphenylene ether in a
single pass single stage system using up to 15 percent water and vacuum venting. Although
all three of the above-mentioned methods reduce the amount of volatile substances
in the resin, none of them reduce the amount of volatile odoriferous species down
to a level where such materials are hardly detectable by analytical methods thus providing
that articles made from them are substantially odorless, especially in food packaging
applications.
[0004] Commonly assigned U.S. patent application of Banevicius, Serial No. , filed
herewith, attorney's docket 335-2134 (8CN-8363), discloses a method for producing
polyphenylene ether resin with a reduced content of phenolic by-products of the polymer
synthesis, such as 2,4,6-trimethylanisole (2,4,6-TMA) and 7-methyldihydrobenzofuran
(7-MDBF) in the initial production stage, but not the reduction of sources of residual
amine components during post-production extrusion stages.
[0005] Commonly assigned U.S. Patent application of Banevicius, Serial No. , filed
herewith, attorney's docket 335-2135 (8CN-8352/83) discloses a method of producing
low odor polyphenylene ether/polystyrene resins by solution blending and employing
a sequence of devolatilizers to reduce the content odoriferous impurities present
in the resin.
[0006] It has now been discovered that if the prior art processes are modified by using
a single pass through an extruder and dividing the water injection/vacuum venting
stage into at least two stages, each consisting of at least one water injection step
and at least one vacuum venting step, remarkable and highly unexpected reductions
in volatile content and in sources of odoriferous amine content are achieved. By way
of illustration, in comparison with a single pass, single stage extrusion, a polyphenylene
ether composition containing 8.5 ppm of 2,4,6-trimethylanisole (TMA) is reduced to
2.6 ppm, but in a single pass, two stages, the TMA content is reduced to levels barely
detectable by gas chromatography (0.27 ppm). If a 50:50 blend of polyphenylene ether
and polystyrene is sent through an extruder in a single pass, single stage with 3
percent water injection and vacuum venting, the styrene content is reduced to 1130
ppm and the toluene content is reduced to 271 parts per million; a back-to-back repitition
using a single pass but two water injection/vacuum venting stages, using 1.5% by
weight of water in each such stage, reduced the styrene content to 694 ppm and toluene
content to 84 parts per million.
[0007] Furthermore, it has been surprisingly discovered that the use of a polyphenylene
ether resin essentially free of phenolic by-products in the improved process of the
present invention produces a resin with a very low content of any odoriferous components.
This novel low odor resin can then be shaped into pellets for further processing or
directly into solid sheets, molded or extruded articles, and foams which are highly
desirable for use in food contact applications.
DESCRIPTION OF THE DRAWING
[0008]
The drawing is illustrative of the apparatus which may be used to carry out the present
invention. It illustrates a vertical cross section of a twin screw extruder having
two stages of water injection each of which has its own vacuum venting stages.
SUMMARY OF THE INVENTION
[0009] According to the present invention there is provided an improved process for the
reduction of volatile substances in a composition comprising
(a) a polyphenylene ether resin, alone, or in combination with
(b) a styrene resin, said composition comprising impurities selected from styrene
monomer, toluene, sources of volatile odoriferous amines, volatile odoriferous oxygenated
species, mixtures of any of them and the like, said process comprising extruding said
composition at a temperature above its melting point in one pass in at least two stages,
each said stage comprising water injection followed by vacuum venting, the total amount
of water being divided between said stages and comprising up to about 15 percent by
weight of said composition whereby the devolatilization efficiency of both toluene
and trimethylanisole is greater than about 70 percent in comparison with the reduction
obtained with the same composition in one pass in a single stage employing the same
amount of water.
[0010] The water can, for example, comprise liquid water or steam. Carbon dioxide can also
be used instead of water. Preferably the polyphenylene ether resin comprises poly(2,6-dimethyl-1,4-phenylene
ether), poly (2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene ether) or a mixture thereof,
but may also comprise a functionalized polyphenylene ether wherein the functionalizing
agent comprises fumaric acid, maleic anhydride, citric acid, trimellitic anhydride
acid chloride or a mixture of any of the foregoing. Preferably the styrene resin comprises
a polystyrene homopolymer or a rubber modified polystyrene.
[0011] Nucleating agents selected from an organic or inorganic particulate material or a
mixture thereof may be added in an effective amount, preferably talc up to about 2
percent by weight of the composition. This appears to favorably induce bubble formation
and thereby increase surface area during devolatilization.
[0012] Preferably the total amount of water to be injected into the extrudate is from about
1 to about 10 percent by weight of said composition, divided equally or unequally
between the stages, and the pressure of the vacuum vents is set such that vapor velocity
through the vent is kept below about 5-6 meters sec⁻¹.
[0013] Preferred embodiments of the present invention also provide a process wherein the
polyphenylene ether resin comprises a low odor polyphenylene ether resin comprising
a 2,4,6-trimethylanisole content of less than about 50 parts per million by weight
based on said resin and a source of amine content of greater than about 10,000 parts
per million based on said resin. Preferably the low odor polyphenylene ether resin
is prepared by oxidatively coupling a phenol in the presence of a catalyst in a solvent
comprising a normally liquid aromatic hydrocarbon in a polymerization zone until formation
of said resin and by-products are substantially complete and recovering said resin
by the addition of a C₁ to C₆ alcohol to the polymer solution and recovering said
aromatic hydrocarbon containing said by-products and distilling to reduce the content
of said by-products and thereafter recycling said aromatic hydrocarbon essentially
free of said by-products to the polymerization zone.
[0014] Among the preferred features of the present invention comprise processes for shaping
the low odor composition into pellets, foamed boards or sheets, solid sheets, molded
or extruded articles and the like.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The polyphenylene ethers (also known as polyphenylene oxides) used as component (a)
in the present invention are a well known class of polymers and are disclosed in Hay,
U.S. 3,306,874 and 3,306,875.
[0016] The polyphenylene ethers favored for use in the practice of this invention generally
contain structural units of the following formula

in which, independently, each Q₁ is hydrogen, halogen, primary or secondary lower
alkyl containing up to 7 carbon atoms, phenyl, haloalkyl or amino alkyl wherein at
least two carbon atoms separate the halogen or nitrogen atom from the benzene ring,
hydrocarbonoxy, or halohydrocarbonoxy wherein at least two carbon atoms separate
the halogen and oxygen atoms; and each Q₂ is independently hydrogen, halogen, primary
or secondary lower alkyl, phenyl, haloalkyl, hydrocarbonoxy or halohydrocarbonoxy
as defined in Q₁. Examples of suitable primary lower alkyl groups are methyl, ethyl,
n-propyl, n-butyl, isobutyl, n-amyl, isoamyl, 2-methylbutyl, n-hexyl, 2,3-dimethylbutyl,
2-, 3- or 4-methylpentyl and the corresponding heptyl groups. Examples of secondary
lower alkyl groups are isopropyl, sec-butyl and 3-pentyl. Preferably, any alkyl radicals
are straight chain rather than branched. Most often each Q₁ is alkyl or phenyl, especially
C₁₋₄ alkyl, and each Q₂ is hydrogen.
[0017] Both homopolymers and copolymers are included in the foregoing description. Suitable
homopolymers are those containing, for example, 2,6-dimethyl-1,4-phenylene ether units.
Suitable copolymers include random copolymers containing such units in combination
with, for example, 2,3,6-trimethyl-1,4-phenylene ether units. Many suitable random
copolymers, as well as homopolymers, are disclosed in the patent literature including
the various Hay patents. Also contemplated are graft copolymers, including those prepared
by grafting onto the polyphenylene ether chain such vinyl monomers as acrylonitrile
and vinyl aromatic compounds (for example, styrene) and such polymers as polystyrenes
and elastomers. Still other suitable polyphenylene ethers are the coupled polyphenylene
ethers in which the coupling agent is reacted with the hydroxy groups of the two polyphenylene
ether chains to increase the molecular weight of the polymer. Illustrative of the
coupling agents are low molecular weight polycarbonates, quinones, heterocycles and
formals.
[0018] The polyphenylene ether generally has a molecular weight (number average, as determined
by gel permeation chromatography, whenever used herein) within the range of about
5,000 to 40,000. The intrinsic viscosity of the polymer is usually in the range of
about 0.30 to 0.6 deciliters per gram (dl/g) as measured in solution in chloroform
at 25°C.
[0019] The polyphenylene ethers are typically prepared by the oxidative coupling of at least
one corresponding monohydroxyaromatic compound. Particularly useful compounds are
2,6-xylenol (wherein each Q₁ is methyl and each Q₂ is hydrogen), whereupon the polymer
may be characterized as a poly(2,6-dimethyl-1,4-phenylene ether), and 2,3,6-trimethylphenol
(wherein each Q₁ and one Q₂ is methyl and the other Q₂ is hydrogen).
[0020] A variety of catalyst systems are known for the preparation of polyphenylene ethers
by oxidative coupling. There is no particular limitation as to catalyst choice and
any of the known catalysts can be used. For the most part, they contain at least one
heavy metal compound such as a copper, manganese or cobalt compound, usually in combination
with various other materials.
[0021] A first class of preferred catalyst systems consists of those containing a copper
compound. Such catalysts are disclosed, for example, in U.S. Patents 3,306,874, 3,306,875,
3,914,266 and 4,028,341. They are usually combinations of cuprous or cupric ions,
halide (i.e., chloride, bromide or iodide) ions and at least one amine.
[0022] Catalyst systems containing manganese compounds constitute a second preferred class.
They are generally alkaline systems in which divalent manganese is combined with such
anions as halide, alkoxide or phenoxide. Most often, the manganese is present as a
complex with one or more complexing and/or chelating agents such as dialkylamines,
alkanolamines, alkylenediamines, omega-hydroxyaromatic aldehydes, o-hydroxyazo compounds,
beta-hydroxyoximes (monomeric and polymeric), o-hydroxyaryl oximes and beta-diketones.
Also useful are known cobalt-containing catalyst systems. Suitable manganese and cobalt-containing
catalyst systems for polyphenylene ether preparation are known in the art by reason
of disclosure in numerous patents and publications.
[0023] The process of this invention may also be employed with functionalized polyphenylene
ethers. These may be prepared by the reaction of at least one functionalizing agent
with a polyphenylene ether. The functionality of the functionalized polyphenylene
ether may be present on the end group; for example, as a result of a reaction with
the phenolic terminal hydroxy group. Functionalization may also involve one of the
aromatic groups in the aromatic rings in the polymer chain, or an alkyl group attached
thereto.
[0024] One method of functionalizing the polyphenylene ether is by reaction with at least
one compound containing (a) a carbon-carbon double or triple bond, hydroxy group,
alkoxy group, arloxy group or acyl halide group, and also (b) a carboxylic acid, acid
salt, acid anhydride, acid amide, acid ester or imido group. A wide variety of such
compounds are suitable for use in the invention. Many illustrative compounds are listed
in U.S. 4,315,086 and U.S. patent application Serial No. 885,497 filed July 14, 1986.
They include maleic, fumaric, itaconic and citraconic acids and their derivatives,
various unsaturated fatty oils and the acids derived therefrom, relatively low molecular
weight olefinic acids such as acrylic acid and its homologs, and the like.
[0025] Other contemplated functionalizing agents are the aliphatic polycarboxylic acids
and derivatives thereof disclosed in U.S. patent application Serial No. 736,489 filed
May 20, 1985. Illustrative polycarboxylic acids of this type are citric acid, maleic
acid and agaricic acid and their esters, amides and salts.
[0026] Still another class of contemplated functionalizing agents are disclosed in U.S.
patent 4,600,741. Illustrative compounds within this class are carboxymethylsuccinic
anhydride acid chloride and trimellitic anhydride acid chloride (TAAC).
[0027] The present invention also includes resin compositions comprising polystyrene resins
in addition to the polyphenylene ether resin. Polystyrene resins are generally added
to the polyphenylene ether resin in order to improve the processability of the resin.
[0028] The polystyrene resins are broadly defined herein and based at least in part from
compounds of the formula

wherein R₁ and R₂ are selected from the group consisting of lower alkyl or alkenyl
groups of from 1 to 6 carbon atoms and hydrogen; R₃ and R₄ are selected from a group
consisting of chloro, bromo, hydrogen and lower alkyl groups of from 1 to 6 carbon
atoms, R₅ and R₆ are selected from a group consisting of hydrogen and lower alkyl
and alkenyl groups of from 1 to 6 carbon atoms or R₅ and R₆ may be concatenated together
with hydrocarbonyl groups to form a naphthyl group.
[0029] Compounds within the above formula include styrene and its homologs and analogs.
In addition to styrene, examples include alpha-methyl styrene, paramethyl styrene,
2,4-dimethyl styrene, chlorostyrene, dichlorostyrene, bromostyrene, dibromostyrene,
p-tert-butyl styrene, p-ethylstyrene, vinylxylene, divinylbenzene and vinylnaphthalene.
Styrene is especially preferred.
[0030] Also contemplated for use in the present invention are rubber modified polystyrenes,
including high impact polystyrenes generally known as HIPS. In general, these modified
polystyrene resins are made by adding rubber or rubber precursors, such as dienes,
polydienes, olefin rubbers, acrylonitrile rubbers, acrylic rubbers and the like, during
or after polymerization of the styrene, to yield an interpolymer of rubber and polystyrene,
a physical admixture of rubber and polystyrene, or both, depending on the particular
process employed.
[0031] Suitable rubber modifiers include polybutadiene, polyisoprene, polychloroprene, ethylene-propylene
copolymers (EPR), ethylene-propylene-diene (EPD) rubbers styrene-butadiene copolymers
(SBR), polyacrylates, polynitriles, mixtures thereof and the like. The amount of rubber
employed will vary, depending on such factors as the process of manufacture and individual
requirements.
[0032] Included within this family of materials for purposes of this invention are more
recently developed forms in which such factors as the rubber particle size, the gel
and cis contents of the rubber phase, and the rubber volume percent are regulated
or controlled to achieve improvements in impact resistance and other properties. These
kinds of rubber modified polystyrenes and HIPS are described in the patent literature,
including Katchman and Lee, U.S. 4,128,602 and Cooper and Katchman, U.S. 4,528,327.
[0033] Also contemplated as suitable for use herein are rubber modified polystyrenes and
HIPS having morphological forms which are sometimes referred to as core-shell, comprising
particles of rubber encapsulated polystyrene dispersed in a matrix of polystyrene
resin. Examples of this type are disclosed in Bennett and Lee, U.S. 4,513,120 as well
as the above-mentioned U.S. 4,528,327.
[0034] Polyphenylene ether (PPE) resins and polystyrene (PS) resins are combinable in all
proportions, e.g., from about 1 to about 99 parts by weight polyphenylene ether and
from about 99 to about 1 part by weight polystyrene. It is contemplated, however,
that low density compositions of the present invention are comprised of at least 2
weight percent PPE, based upon the weight of PPE and PS taken together. Compositions
containing less than 2 weight PPE are considered to be primarily polystyrene compositions
and do not generally exhibit the preferred property improvements associated with PPE/PS
blends. It is well known that the addition of PPE to polystyrene resins offers improvements
in impact strength, flammability ratings, tensile strength and other mechanical properties.
Conversely, polystyrene is typically blended with polyphenylene ether resins to offer
better processability for many thermoplastic processes.
[0035] Typical PPE/PS blends useful in the practice of the present invention will be comprised
of between 5 to 95 percent and preferably 20 to 80 percent by weight PPE and 95 to
5 percent and preferably 80 to 20 percent by weight PS based upon the weight of the
two resins taken together.
[0036] It is also contemplated in the present invention to add an effective amount of an
organic or inorganic particulate material as a nucleating agent to the resin composition
to induce bubble formation and increase surface area during devolatilization. One
can use ground glass, carbon black, talc, and the like. Preferably the nucleating
agent comprises talc in an amount of up to about 2 percent by weight based on said
resin composition.
[0037] An essential step in the method of this invention is extrusion of the polyphenylene
ether composition with styrene resin. Extrusion may be conducted using any known equipment
for this operation, including single-screw and twin-screw extruders. See, for example,
Modern Plastics Encyclopedia/88, October 1987, McGraw Hill, New York, p. 228 - 238.
Especially suitable for amine removal is a co-rotating twin screw extruder.
[0038] Since multiple stages of water injection and vacuum venting are also essential features
of this invention, the presence of suitable ports in the extruder for injection of
a stripping agent and vents for vacuum venting are mandatory. The stripping agent
may be introduced at any point upstream of the first vent or set of vents; however,
it is highly preferred to introduce the stripping agent through a port located at
a point in the extruder where the polymer composition has been converted into a fully
developed polymer, since this facilitates intimate contact with the polymer.
[0039] Water or steam are the preferred stripping agents, and the proportion employed is
up to about 15 percent by weight of the polymer composition, to be divided equally,
or unequally, among the two or more injection ports located along the length of the
extruder barrel. The preferred proportion is about 1 - 10 percent, since an amount
within this range is generally optimally effective for removal of volatiles without
burdening the vacuum system. For example, where two injection ports are present and
about 5 percent total water by weight of polymer composition is to be used, each injection
port would inject about 2½ percent of the water into the extrudate.
[0040] The degree of vacuum will depend on several factors, including the proportion of
volatile impurities in the polyphenylene ether or polyphenylene ether/poly styrene
resin and the amount of water to be employed. In general, it is preferable to limit
the vapor velocity across the vent interface to about 5-6 meters sec⁻¹ and the pressure
should be set accordingly.
[0041] In most instances, maximum or near maximum rate of rotation of the extruder screw
or screws should be maintained for effective volatilization. The rotation rate will
to some extent be dependent on the equipment used, but values in the range of about
300 to about 500 revolutions per minute are generally sufficient.
[0042] Referring to the drawing, extruder 1 comprises a heated barrel 2 and a multi-flight
screw 4 adapted to co-rotate with a twin screw (not shown). Feed hopper 6 located
at the upstream end is adapted to receive polyphenylene ether or polyphenylene ether
and polystyrene and any conventional additives and, if desired, a nucleating agent,
such as talc. As the resin moves downstream, it is heated and melted. The resin melt
then encounters stage 20 comprising water injection port 8 and vacuum vents 10 and
12. The resin melt which exits stage 20 immediately encounters the second stage 22
comprising water injection port 14 and vacuum vents 16 and 18. Finally, the material
exits the extruder at front barrel outlet 24. The exiting product can be extruded
into shapes or cut into pellets for further processing in accordance with conventional
techniques.
[0043] It is further contemplated to employ a polyphenylene ether resin essentially free
from phenolic odoriferous by-products of polymer synthesis, such as 2,4,6-trimethylanisole
and 7-methyldihydrobenzofuran, removed from the normally liquid aromatic hydrocarbon
recycle stream by distillation. The distillation may be performed in any suitable
distillation column. The recycle aromatic hydrocarbon stream is fed into a column
shell comprising various plates or trays, which are used to bring the vapor and liquid
phases of the feed material into intimate contact, stacked one above the other inside
the enclosed column. Optionally, a packed column may be employed. The aromatic hydrocarbon
solution is boiled and the purified aromatic hydrocarbon vapor is collected and condensed
at the top of the column, while the impurities remain liquid and are collected at
the bottom of the column. The number of trays necessary is dependent upon the degree
of purity desired in the distillate and the type of tray used. Suitable for the practice
of this invention are distillation columns employing sieve type trays ranging from
about 40 to about 65 in number.
[0044] Distillation is carried out to render the recycle aromatic hydrocarbon essentially
free of by-product content. Essentially free is defined as the level of odoriferous
impurities present in the recycle aromatic hydrocarbon such that recycling the aromatic
hyrocarbon to the polymerization zone results in a very low odor product resin, not
detectable by individuals with highly developed olfactory systems. Preferably, the
2,4,6-trimethylanisole content in the recycle aromatic hydrocarbon is reduced to less
than about 5 parts per million and the 7-methyldihydrobenzofuran is reduced to less
than about 50 parts per million.
[0045] Other embodiments of the process of the present invention, include shaping the low
odor composition into pellets, solid sheets, foamed sheets or boards, molded or extruded
articles and the like.
[0046] Any conventional hot or cold pelletizing or dicing systems may be used to form pellets.
Cold cutting systems are generally dicing, strand pelletizing and strand (forced conveyance)
pelletizing systems. Hot cutting systems generally comprise water ring pelletizers,
hot face pelletizers, underwater pelletizers and centifuged pelletizers. See generally
Modern Plastics Encyclopedia/88, McGraw-Hill, 1987, pp. 340-342. Solid sheets are
generally formed by extending the molten composition through dies specially suited
for forming solid sheets, such as flat sheet dies, although any die which will produce
a solid sheet may be employed. See generally, Modern Plastics Encyclopedia/88, McGraw
Hill, 1987, pp. 236-237. Extruded or molded articles may be produced in any conventional
process and apparatus known to those skilled in the art.
[0047] Optionally, the low odor composition may be foam processed. Any suitable apparatus
for extruding foamed sheets or boards may be employed in this shaping process. See
for example, Modern Plastics Encyclopedia/88, McGraw Hill 1987, pp 238-246. Especially
suitable for the practice of the present invention are tandem extruders. The resin
composition is fed into a first mixing-melting single or twin screw type extruder
and melted and mixed therein with a liquid blowing agent at sufficient temperature
and shear to provide an intimate blend.
[0048] During the blending step it is also contemplated to introduce conventional additives
into the polymer composition melt. These include nucleating agents, flame retardants,
thermal and color stabilizers, antioxidants, processing aids, plasticizers, reinforcing
and extending fillers, pigments, dyes and the like. Each of these may be utilized
to a greater or lesser degree depending on the desired final properties of the foamed
product. Conventional surfactants and nucleants may also be utilized, such as zinc
or tin stearates, maleates and fumarates.
[0049] Suitable nucleating agents, which aid in controlling the foam cell size and number
of foam cells, usually comprise a fine powder such as talc or a combination of citric
acid and bicarbonate of soda.
[0050] Suitable blowing agents to be used in the melt produced in the extruder include conventional
hydrocarbons, chlorofluorocarbons, and hydrochlorofluorocarbons. Hydrocarbon blowing
agents will include aliphatic hydrocrbons, especially those having 4 to 7 carbon atoms
such as pentane, isopentane, pentene, hexane, heptane, butane and the like. Chlorofluorocarbon
blowing agents include CCl₃F, CCl₂F₂, C₂Cl₃F₃, C₂ClF₅, CHClF₂ and CCl₂F₂-CClF₂. These
are comercially available as Freon® 11, Freon® 12, Freon® 22, Freon® 113, Freon® 115
and Freon® 114. Hydrochlorofluorocarbon blowing agents include compounds such as chlorodifluoromethane,
dichlorofluoromethane, dichlorodifluoroethane and the like.
[0051] Although the extrudate can be foamed through a die in the first extruder, preferably
the extrudate is transferred through a pressurized closed conduit to a second single
or twin screw extruder.
[0052] The conduit should be heated to maintain melt consistency. In the second extruder,
the melt is cooled and exits as a foam at a die located at the downstream end of the
extruder barrel.
[0053] As an alternative, the blowing agent can also be introduced into the devolatilizing
extruder to obtain a melt which contains the liquid blowing agent under pressure.
This material can be foamed directly out a die at the downstream end of the devolatilizing
extruder or may be transferred to single or tandem foam extruders for foaming.
[0054] Also contemplated by the present invention is combining the low odor composition
of the present invention with let-down resins, including polyphenylene ether resins,
prior to further processing or shaping. Resins such as a polystyrene, a rubber modified
polystyrene, copolymers of styrene and acrylonitrile, a poly(butylene terephthalate),
a poly(bisphenol-A carbonate), a poly(etherimide ester), a poly(ester carbonate),
a polyamide resin, ABS resins, and the like, or a mixture of any of them can be used
as let-down resins.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0055] The following examples illustrate the present invention. They are not to be construed
to limit the claims in any manner whatsoever.
EXAMPLE 1
[0056] A poly(2,6-dimethyl-1,4-phenylene ether)/polystyrene homopolymer blend comprising
about 50 parts by weight of each resin component is fed into an extruder equipped
with a two stage water injection/vacuum venting system at a rate of 318 kg/hr, a
screw speed of 350 rpm, barrel temperature setpoints at 343°C, a melt temperature
of 360°C wherein water is injected at a rate of 1.5 weight percent of the feed at
each injection port and the vacuum pressure set at about 130 - 150 mbar. The starting
material contains 9 ppm of TMA, 0.5 percent of DBA and 1500 ppm of toluene. A control
sample is fed into a single stage water injection vacuum venting system extruder at
the same processing parameters except that water is injected at 3 weight percent of
the feed rate through the single injection port. The results of volatile substance
removal are set forth below in Table 1.
TABLE 1
VOLATILES REDUCTION 50/50 PPE/PS EXTRUDATE |
Examples |
1* |
1 |
EXTRUDER PARAMETERS |
|
|
Feed Rate, kg/hr |
318 |
318 |
Screw Speed, rpm |
350 |
350 |
Barrel Temp., °C |
343 |
343 |
Melt Temp., °C |
360 |
360 |
Water Injection Rate, % |
3 |
1.5 |
Vacuum Pressure, mbar |
130 - 150 |
130 - 150 |
EXTRUDATE VOLATILES |
|
|
Styrene monomer, ppm |
1130 |
694 |
Toluene, ppm |
271 |
84 |
DBA, % |
0.18 |
0.15 |
TMA,ppm |
2.6 |
0.27 |
7-MDBF |
3.3 |
0.1 |
* Control Sample |
DBA = di-butyl amine |
TMA = 2,4,6-trimethylanisole |
7-MDBF = 7-methyldihydrobenzofuran |
[0057] The table clearly shows that using an equal amount of water in a two stage process
results in a vastly greater reduction of volatile impurities from the extrudate than
can be accomplished in a one stage process.
EXAMPLE 2
[0058] A resin composition comprising 70 parts by weight of poly(2,6-dimethyl-1,4-phenylene
ether) and 30 parts by weight of polystyrene homopolymer is fed into an extruder equipped
with a single stage water injection vacuum venting system at a rate of 81.8 kg/hr,
a screw speed of 350 RPM, barrel temperature setpoints at 315°C, wherein water is
injected at a rate of 2.5% and 5% and the vacuum pressure is set at 35 mbar. The resin
composition contains about 0.7% DBA by weight and also 175 ppm TMA by weight. A resin
composition containing 20 ppm of TMA is extruded under the same conditions, except
that water is injected at a rate of 2.5 weight % of the feed at each of two water
injection ports. The results of volatile substance removal are set forth below in
Table 2.
TABLE 2
EXTRUDER PARAMETERS |
2A* |
2B* |
2C* |
2 |
Feed rate, kg/hr |
82 |
82 |
82 |
82 |
Screw speed, rpm |
350 |
350 |
350 |
350 |
Barrel Temp., °C |
315 |
315 |
315 |
315 |
Water injection rate, % |
2.5 |
5 |
0 |
5 |
Number of injection stages |
1 |
1 |
0 |
2 |
Vacuum pressure, mbar |
35 |
35 |
35 |
70 |
FEEDSTOCK VOLATILES |
|
|
|
|
TMA, ppm |
175 |
175 |
175 |
20 |
DBA, wt. % |
0.7 |
0.7 |
0.7 |
0.7 |
% TMA removed |
85 |
86 |
80 |
97 |
EXTRUDATE VOLATILES |
|
|
|
|
TMA, ppm |
26 |
24 |
34 |
0.5 |
DBA, wt. % |
0.32 |
0.31 |
0.37 |
0.17 |
% TMA removed |
85 |
86 |
80 |
97 |
* = Control Sample |
TMA = 2,4,6-trimethylanisole |
DBA = di-butyl amine |
wppm = weight parts per million |
[0059] The table clearly shows using an equal amount of water in a two stage process results
in a vastly greater reduction of volatile impurities from the extrudate than can be
accomplished in a one-stage process.
EXAMPLE 3
[0060] The procedure of Example 2 is repeated for a resin composition comprising 49 parts
by weight of poly(2,6-dimethyl-1,4-phenylene ether), 49 parts by weight of polystyrene
homopolymer and 2 parts by weight of talc. Many tiny bubbles are created in the vacuum
vented section. The extrudate is comminuted into pellets and the pellets are odorless.
Without talc, occasional individuals with highly developed olefactory systems sometimes
state that the pellets are slightly odorous. When molded into soup containers, the
products of this example pass the soup taste test, a very discriminating test for
low odor in food packaging.
[0061] The above-mentioned patents, applications and publications as well as test methods
are incorporated herein by reference.
[0062] Many variations of the present invention will suggest themselves to those skilled
in this art in light of the above detailed description. For example, instead of polyphenylene
ether in Example 1, a mixture of 100 parts of polyphenylene ether and 0.7 parts of
fumaric acid can be fed into the extruder and a functionalized polyphenylene ether
with a very low odoriferous amine content can be obtained. Instead of poly(2,6-dimethyl-1,4-phenylene
ether), a poly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene ether) can be used.
Additionally, a low odor polyphenylene ether resin may be employed. A three stage
extrusion can be used in which the first stage comprises carbon dioxide injection
followed by vacuum venting, followed by two water injection vacuum venting stages.
Steam can be used instead of water. All such obvious variations are within the full
intended scope of the appended claims.
1. A process for the reduction of volatile substances in a composition comprising
(a) a polyphenylene ether resin, alone, or in combination with
(b) a styrene resin, said composition comprising impurities selected from styrene
monomer, toluene, volatile odoriferous oxygenated species, sources of volatile odoriferous
amines, mixtures of any of them and the like, said process comprising extruding said
composition at a temperature above its melting point in one pass in at least two stages,
each said stage comprising water injection followed by vacuum venting, the total amount
of water being divided between said stages and comprising up to about 15 percent by
weight of said composition whereby the devolatilization efficiency of both toluene
and trimethylanisole is greater than about 70 percent in comparison with the reduction
obtained with the same composition in one pass in a single stage employing the same
amount of water.
2. A process as defined in Claim 1 wherein said composition comprises polyphenylene
ether, alone.
3. A process as defined in Claim 1 wherein said polyphenylene ether resin component
(a) comprises poly(2,6-dimethyl-1,4-phenylene ether), poly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene
ether) or a mixture thereof.
4. A process as defined in Claim 1 wherein said styrene resin component (b) comprises
a polystyrene homopolymer resin.
5. A process as defined in Claim 1 wherein said styrene resin component (b) comprises
a rubber modified styrene polymer.
6. A process as defined in Claim 1 wherein said polyphenylene ether resin component
(a) comprises a functionalized polyphenylene ether.
7. A process as defined in Claim 6 wherein said functionalizing agent is fumaric acid,
maleic anhydride, citric acid, trimellitic anhydride acid chloride or a mixture of
any of the foregoing.
8. A process as defined in Claim 7 wherein said functionalizing agent is maleic anhydride.
9. A process as defined in Claim 1 wherein the temperature in the extruder is above
about 280°C and the water injected comprises liquid water.
10. A process as defined in Claim 1 wherein the temperature in the extruder is above
about 280°C and the water injected comprises steam.
11. A process as defined in Claim 1 wherein the total amount of water injected is
from about 1 to about 10 percent by weight of the polymer composition.
12. A process as defined in Claim 1 wherein the pressure during extrusion is in the
range of about 550 to about 720 torr.
13. A process as defined in Claim 1 wherein an effective amount of a nucleating agent
selected from an organic or an inorganic particulate material or mixture thereof is
addded to the composition to induce bubble formation and increase surface area during
devolatilization.
14. A process as defined in Claim 13 wherein said nucleating agent comprises talc
in an amount of up to about 2 percent by weight based on said composition.
15. A process as defined in Claim 1 including the step of injecting carbon dioxide
into the extruder in at least one injection stage.
16. A process as defined in Claim 1 including setting the pressure of the vacuum vent
such that the vapor velocity through the vent is kept below about 5-6 meters sec⁻¹.
17. A process as defined in Claim 1 wherein said polyphenylene ether resin component
(a) comprises from about 5 to about 95 parts by weight and said polystyrene resin
component (b) comprises from about 95 to about 5 parts by weight.
18. In a process for the reduction of volatile substances in a composition comprising
(a) a polyphenylene ether resin, alone, or in combination with
(b) a styrene resin, said composition comprising impurities selected from styrene
monomer, toluene, volatile odoriferous oxygenated species, sources of volatile odoriferous
amines, mixtures of any of them, and the like; said process comprising extruding said
composition at a temperature above about 280°C in one pass in the presence of water
followed by vacuum venting, the improvement which comprises carrying out the process
in at least two stages each said stage comprising water injection followed by vacuum
venting, the total amount of water being divided between said stages and comprising
up to about 15 percent by weight of said composition, whereby the devolatilization
efficiency of both toluene and trimethylanisole is greater than about 70 percent in
comparison with the reductions obtained with the same composition in one pass in a
single stage employing the same amount of water.
19. A process as defined in Claim 1 wherein said polyphenylene ether resin comprises
a low odor polyphenylene ether resin having a 2,4,6-trimethylanisole content of less
than about 50 parts per million by weight based on said resin and sources of odoriferous
amine content of greater than about 10,000 parts per million based on said resin.
20. A process as defined in Claim 19 wherein said low odor polyphenylene ether resin
is prepared by oxidatively coupling a phenol in the presence of a catalyst in a solvent
comprising a normally liquid aromatic hydrocarbon in a polymerization zone until formation
of said resin and by-products are substantially complete and recovering said resin
by the addition of a C₁ to C₆ alcohol to the polymer solution and recovering said
aromatic hydrocarbon containing said by-products and distilling to reduce the content
of said by-products and thereafter recycling said aromatic hydrocarbon essentially
free of said by-products to the polymerization zone.
21. A process as defined in Claim 20 wherein said phenol feed into the reactor comprises
2,6-xylenol.
22. A process as defined in Claim 20 wherein said normally liquid aromatic hydrocarbon
comprises toluene.
23. A process as defined in Claim 20 wherein said distilling comprises distilling
said aromatic hydrocarbon and said by-products to reduce the content of 2,4,6-trimethylanisole
by-product present in said aromatic hydrocarbon to less than about 5 weight parts
per million based on said aromatic hydrocarbon.
24. A process as defined in Claim 19 wherein said polyphenylene ether resin comprises
a by-product 7-methyldihydrobenzofuran content of about 0.5 to about 50 weight parts
per million based on said resin.
25. A process as defined in Claim 19 which also comprises step (c) comprising shaping
the low odor composition.
26. A process as defined in Claim 25 wherein said step (c) comprises pelletizing said
low odor composition.
27. A process as defined in Claim 25 wherein said step (c) comprises foaming said
low odor composition.
28. A process as defined in Claim 27 wherein said step (c) comprises
(i) feeding said low odor composition into at least one extruder and mixing it with
a blowing agent; and
(ii) foaming the mixture through a die to form a shaped, foamed sheet or board having
very low odor in human organoleptic tests.
29. A process as defined in Claim 28 wherein said step (i) comprises feeding said
composition into tandem extruders, the first extruder being adapted to melt and mix
said composition and said blowing agents into the polymer melt and the second extruder
is adapted for cooling the melt prior to foaming.
30. A process as defined in Claim 28 wherein said blowing agent comprises a hydrocarbon,
a chlorofluorocarbon, a hydrochloroflourocarbon or a mixture thereof.
31. A process as defined in Claim 30 wherein said blowing agent comprises chlorodifluoromethane.
32. A process as defined in Claim 28 which also comprises adding a nucleating agent
in step (i) in an amount sufficient to aid in regulating the size of foam cell and
number of foam cells.
33. A process as defined in Claim 25 wherein said step (c) comprises extruding said
composition through a suitable die to form a solid sheet having very low odor in human
organoleptic tests.
34. A process as defined in Claim 25 wherein said step (c) comprises
(i) adding said blowing agent directly into the extruder of step (b) to yield a low
odor composition containing a liquid blowing agent under pressure; and
(ii) feeding said low odor composition into an extruder equipped with a foaming die;
and
(iii) foaming said composition through said die to form a shaped foamed sheet or board
having very low odor in human organoleptic tests.
35. A process as defined in Claim 25 wherein said step (c) comprises extruding said
composition through a suitable die to form an extruded article having very low odor
in human organoleptic tests.
36. A process as defined in Claim 25 wherein said step (c) comprises molding said
composition to form a molded article having very low odor in human organoleptic tests.
37. A low odor polyphenylene ether or polyphenylene ether/polystyrene pellet produced
by the process as defined in Claim 26.
38. A low odor polyphenylene ether or polyphenylene ether/polystyrene foamed sheet
or board produced by the process as defined in Claim 28.
39. A low odor polyphenylene ether or polyphenylene ether/polystyrene solid sheet
produced by the process as defined in Claim 33.
40. A low odor polyphenylene ether or polyphenylene ether/polystyrene extruded article
produced by the process as defined in Claim 35.
41. A low odor polyphenylene ether or polyphenylene ether/polystyrene molded article
produced by the process as defined in Claim 36.